The UN's high commissioner for refugees, António Guterres, has said that his agency has less than half the money it needs to look after hundreds of thousands of Africans driven from their homes by conflict and forgotten by the international community, and may have to start cutting its spending on education and repatriation.

Guterres said that as international attention and sympathy had drifted away from Africa, the UNHCR had so far managed to keep its African operations going by using money saved by cutting overheads at its headquarters in Geneva, but those funds had run out.

As the Syrian civil war has increasingly dominated the headlines, world attention has drifted away from intractable conflicts in Africa and the refugee populations they have created, Guterres said.

"All our African operations are substantially underfunded," he told the Guardian. "In Chad, we have about 280,000 Darfurian refugees, not to mention the 60,000 refugees from the Central African Republic who are in the south of Chad. Four or five years ago, Darfur was very much under the attention of the international community. It was one of the best funded operations we had."

By contrast, the UNHCR currently has only a quarter of the $177m (£110m) needed to provide for the refugees in Chad. Funds needed for emergencies in the Democratic Republic of the Congo and the Sahel are also severely undersubscribed. Of the $1.9bn required for refugees across the whole continent, only a third has been forthcoming from donors, a reflection of how the problem has slipped from the global agenda. To make up the shortfall, the UNHCR has been using funds freed by efficiency savings, but it is not a permanent solution.

"We have dramatically reduced our overheads. In Geneva we had a staff of 1,000 and now we have less than 700. That has allowed us to use un-earmarked money that might otherwise have been used in headquarters to be used in these forgotten emergencies," Guterres said. He added that that still left budgets far short of needs, and "now we have exhausted all our reserves" and the only alternative was to start cutting support to refugees.

"Obviously, if at a certain moment we are not able to maintain the same level of funding, we will have to start cutting a certain number of services, which is something we don't want to do, because it has to do with not only with basic needs of people but also their dignity," Guterres said. "Of course, we will always maintain the life-saving activities but people … do not only need water and food and shelter. They also need education, and self-reliance in their life, and these are the sort of investments that are totally impossible, forcing us to restrain our activities to core life-saving and protection action, which is not what we want."

The cuts will also mean an end to investment in the refugees' devastated home towns and villages that would have encouraged voluntary returns and thus a long-term decline in refugee numbers. Earlier this year, there were reports of the return of about 100,000 internally displaced people from camps inside Darfur to their home villages, but Guterres said there had been a very small decline in the number of Darfur refugees over the border in Chad.